Ribbons Theme – Show excerpts in categories, content in main

Hey there,

I am asking here because the theme author closed his help forum I hope you can help me!

I’m using the Ribbons Theme by AJ Clarke on https://www.goldene-speichen.de. I can not find out how to show the full post on the main/index site and excerpts only on the category/archive sites.

He put the <?php the_content(); ?> into the post-entry.php, changing this to <?php the_excerpt(); ?> results in showing everything in full-content.

Thank you in advance ??